Pollution concentrations recorded by the LAQN analysers have been classified according to Defra's
Air Pollution Index system. This classes levels into bands from 'low' to 'very high'. Each band is subdivided into three to produce
an Air Pollution Index, from 1 to 10, 1 being 'low', 10 being 'very high'. Measurements are rounded to the nearest whole number. The concentrations are classified according to
the table above. Note that different pollutants have different concentrations and averaging periods, related to the
estimated health effects of each.